This invention relates to a toner residual amount detecting circuit associated with a toner supply mechanism in a dry type electrophotographic apparatus.
A developing agent for use in a dry type electrophotographic apparatus generally consists of a toner which is deposited onto a latent image of a photoconductive drum and a carrier for carrying the toner, or a toner alone. Such a toner is consumed by development and it is necessary to supply a toner. Recently an electrophotographic apparatus is connected to a computer and it is used as an output device of the computer. There arises the necessity of detecting a residual amount of toner.
A toner residual amount detecting device is known which is adapted to detect a residual amount of toner in a toner hopper by its weight. The device is adapted to detect a residual amount of toner in response to the operation of a microswitch adapted to be opened when the whole weight of the toner-filled hopper is lowered to below a predetermined level. Since in such device the toner hopper is required to be floated, a holding mechanism for the toner hopper becomes complicated in design.
Another residual amount detecting device is adapted to detect a toner-carrier mixed ratio of the developing agent by a variation in the inductance of a coil embedded in the developing agent.
Another residual amount detecting device is adapted to magnetically detect a residual amount of toner. According to this magnetic device a magnet is disposed at the lower portion of a toner hopper in which magnetized carrier and toner are received. When the magnet is attracted toward, and repelled from, the toner hopper in accordance with an amount of toner in the toner hopper a microswitch is operated in accordance with the movement of the magnet and a residual amount of toner is detected according to the operation of the microswitch.
In the last-mentioned two devices a residual amount can not be detected if a developing agent consists of a toner alone.